Burma's pro-democracy leader Aung San Suu Kyi has fallen ill while campaigning for forthcoming by-elections and has suspended her extensive tour of the country a week before the polls, her party says.

Kyi Toe, deputy information officer for the National League for Democracy (NDL), said on Sunday that Aung San Suu Kyi's personal physician advised taking the break after she started vomiting while campaigning in the Mergui archipelago in southern Burma.

The doctor, Tin Myo Win, who was accompanying Aung San Suu Kyi, said her ill health was due to exhaustion and the hot weather, according to Kyi Toe. Party members travelling with the 66-year-old Nobel peace prize laureate said she was put on an intravenous drip.

Released from house arrest in 2010, Aung San Suu Kyi has travelled by car, plane and boat to campaign around the country. She is running in a constituency south of Rangoon.

The polls are the first in which the NLD is taking part since it won a 1990 general election only to have the army refuse to let it take power, triggering two decades of military repression. They are seen as an indicator of political reforms by Burma's current military aligned government since a 2010 election that the opposition boycotted.

Aung San Suu Kyi fell ill on Saturday during a gruelling day of boat travel that saw her vessel go temporarily aground. NLD members, who asked not to be identified because they were not authorised to speak to the media, said the authorities denied her party the use of a larger ferry-type vessel that would have allowed her to travel faster, so her group was forced to use three smaller boats, which made the journey's duration three times as long.

Despite her illness, Aung San Suu Kyi briefly addressed a crowd of 10,000 people on Sunday in Mergui, mentioning the problem in obtaining a fast boat and promising to return when she is well. She has generally drawn large and enthusiastic crowds on the campaign trail, aside from appearances near the capital, Naypyitaw, whose large population of civil servants and soldiers owe their living to the government.

She and her party have charged the government with taking measures to handicap her party, such as selective bans on using large public venues including football stadiums. They also have said that voting registries contain the names of dead people, opening up the potential for electoral fraud.

Kyi Toe said Aung San Suu Kyi 's campaigning had been suspended at least until Wednesday, when she was scheduled to be in central Burma, where one of her intended destinations was Natmauk, the hometown of her late father, independence hero General Aung San. It is unclear if she will be able to make a scheduled overnight before the polls in Kawhmu, the constituency where she is running.

There were 48 seats at stake in the by-elections, but the state election committee announced on Friday that voting would be postponed in three constituencies of Kachin state, where there has been sporadic but sometimes fierce fighting between government troops and ethnic Kachin rebels, who have long sought more autonomy and faced increased crackdowns this past year. The NLD intended to contest all 48 seats, though one of its candidates was disqualified.

The NLD's participation in the April vote is seen as an endorsement of President Thein Sein's reforms, though Aung San Suu Kyi has declared that much more needs to change before the country can claim to be democratic.

The opposition boycotted the 2010 general election, saying it was neither free nor fair, leaving the field open for a landslide victory by the army-backed Union Solidarity and Development party and the installation of Thein Sein – the former junta's prime minister – as president.

Thein Sein initiated reforms, including the release of political prisoners, and the NLD agreed to rejoin electoral politics after election laws were changed to meet its objections.